Find a new pair of pants for Charles.
Activate the event by jumping into Charles who is found stuck in the Phoenix Mountain. He will thank Tomba for rescuing him and then ask him to find his extra pair of pants that he lost, since the ones he is wearing has been torn.
Make your way to the entrance to the Lava Caves and head inside. Talk to the person and he will give Tomba Charles' pants. Go back to Charles and give him his pants to clear the event.